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The dopamine (DA) hypothesis postulates hyperactivity of subcortical DA transmission and hypoactivity of cortical DA in schizophrenia (SCH). Positron emission tomography provides the ability to assess this hypothesis in humans. However, no studies have examined the relationship between cortical DA and striatal DA in this illness.Dsub2/3/subreceptor radiotracer [sup11/supC]FLB457 BPsubND/sub(binding potential relative to nondisplaceable uptake) was measured in 14 off-medication subjects with SCH and 14 healthy control (HC) subjects at baseline and after the administration of 0.5 mg/kg oral d-amphetamine. The amphetamine-induced change in BPsubND/sub(ΔBPsubND/sub) was calculated as the difference between BPsubND/subin the postamphetamine condition and BPsubND/subin the baseline condition and expressed as a percentage of BPsubND/subat baseline. DA release in the striatum using the radiotracer [sup11/supC]NPA was also measured in these subjects.[sup11/supC]FLB457 ΔBPsubND/subwas greater in the HC group compared with the SCH group (Fsub1,26/sub = 5.7; p = .02) with significant differences in [sup11/supC]FLB457 ΔBPsubND/subseen across cortical brain regions. Only in the SCH group was a significant negative correlation observed between [sup11/supC]FLB457 ΔBPsubND/subin the dorsolateral prefrontal cortex and [sup11/supC]NPA ΔBPsubND/subin the dorsal caudate (r = -0.71, p = .005).Subjects with SCH demonstrated deficits of DA release in cortical brain regions relative to HC subjects. Examining both cortical and striatal DA release in the same subjects demonstrated an inverse relationship between cortical DA release and striatal DA release in SCH not present in HC subjects, providing support for the current DA hypothesis of SCH.

Docosahexaenoic acid (DHA) shows anti-inflammatory/proresolution effects in the brain. Higher red blood cell (RBC) DHA in humans is associated with improved cognitive performance and a lower risk for suicide. Here, we hypothesized that binding to the 18 kDa translocator protein (TSPO), a proxy for microglia levels, will be higher in individuals with low DHA relative to high DHA levels. We also postulated that higher TSPO would predict poor cognitive performance and impaired stress resilience.RBC DHA screening was performed in 320 healthy males. [sup11/supC]PBR28 positron emission tomography was used to measure binding to TSPO in 38 and 32 males in the lowest and highest RBC DHA quartiles. Volumes of distribution expressed relative to total plasma ligand concentration (VsubT/sub) was derived using an arterial input function-based kinetic analysis in 14 brain regions.[sup11/supC]PBR28 VsubT/subwas significantly lower (by 12% and 20% in C/T and C/C rs6971 genotypes) in males with low RBC DHA than in males with high RBC DHA. Regional VsubT/subwas correlated positively and negatively with RBC DHA and serum triglycerides, respectively. No relationships between VsubT/suband cognitive performance or stress resilience measures were present.Contrary to our hypothesis, we found lower TSPO binding in low-DHA than in high-DHA subjects. It is unclear as to whether low TSPO binding reflects differences in microglia levels and/or triglyceride metabolism in this study. Future studies with specific targets are necessary to confirm the effect of DHA on microglia. These results underscore the need to consider lipid parameters as a factor when interpreting TSPO positron emission tomography clinical findings.

Tuberculosis remains a large global disease burden for which treatment regimens are protracted and monitoring of disease activity difficult. Existing detection methods rely almost exclusively on bacterial culture from sputum which limits sampling to organisms on the pulmonary surface. Advances in monitoring tuberculous lesions have utilized the common glucoside [18F]FDG, yet lack specificity to the causative pathogenMycobacterium tuberculosis(Mtb) and so do not directly correlate with pathogen viability. Here we show that a close mimic that is also positron-emitting of the non-mammalianMtbdisaccharide trehalose – 2-[18F]fluoro-2-deoxytrehalose ([18F]FDT) – can act as a mechanism-based enzyme reporter in vivo. Use of [18F]FDT in the imaging ofMtbin diverse models of disease, including non-human primates, successfully co-optsMtb-specific processing of trehalose to allow the specific imaging of TB-associated lesions and to monitor the effects of treatment. A pyrogen-free, direct enzyme-catalyzed process for its radiochemical synthesis allows the ready production of [18F]FDT from the most globally-abundant organic18F-containing molecule, [18F]FDG. The full, pre-clinical validation of both production method and [18F]FDT now creates a new, bacterium-specific, clinical diagnostic candidate. We anticipate that this distributable technology to generate clinical-grade [18F]FDT directly from the widely-available clinical reagent [18F]FDG, without need for either bespoke radioisotope generation or specialist chemical methods and/or facilities, could now usher in global, democratized access to a TB-specific PET tracer.

Tau PET tracers exhibit varying levels of specific signal and distinct off-target binding patterns that are more diverse than amyloid PET tracers. This study compared 2 frequently used tau PET tracers, (18)F-flortaucipir and (18)F-MK-6240, in the same subjects. Methods: (18)F-flortaucipir and (18)F-MK-6240 scans were collected within 2 mo in 15 elderly subjects varying in clinical diagnosis and cognition. FreeSurfer, version 5.3, was applied to 3-T MR images to segment Braak pathologic regions (I–VI) for PET analyses. Off-target binding was assessed in the choroid plexus, meninges, and striatum. SUV ratio (SUVR) outcomes were determined over 80–100 min ((18)F-flortaucipir) or 70–90 min ((18)F-MK-6240) normalized to cerebellar gray matter. Masked visual interpretation of images was performed by 5 raters for both the medial temporal lobe and the neocortex, and an overall (majority) rating was determined. Results: Overall visual ratings showed complete concordance between radiotracers for both the medial temporal lobe and the neocortex. SUVR outcomes were highly correlated (r(2) > 0.92; P ≪ 0.001) for all Braak regions except Braak II. The dynamic range of SUVRs in target regions was approximately 2-fold higher for (18)F-MK-6240 than for (18)F-flortaucipir. Cerebellar SUVs were similar for (18)F-MK-6240 and (18)F-flortaucipir, suggesting that differences in SUVRs are driven by specific signals. Apparent off-target binding was observed often in the striatum and choroid plexus with (18)F-flortaucipir and most often in the meninges with (18)F-MK-6240. Conclusion: Both (18)F-MK-6240 and (18)F-flortaucipir are capable of quantifying signal in a common set of brain regions that develop tau pathology in Alzheimer disease; these tracers perform equally well in visual interpretations. Each also shows distinct patterns of apparent off-target binding. (18)F-MK-6240 showed a greater dynamic range in SUVR estimates, which may be an advantage in detecting early tau pathology or in performing longitudinal studies to detect small interval changes.